1. Field of the Invention
The present invention relates to a tilt steering system, more specifically, to improvement of a component for rockably supporting a steering column which constitutes a steering system for automobiles with respect to a car body, thereby ensuring fixation of the steering column as well as improving rigidity felt by the driver.
2. Related Background Art
As an adjuster unit for adjusting height of a steering wheel, what are called tilt steering systems which can change height of the steering wheel according to the constitution or the driving posture of the driver have been disclosed in, for example, Japanese Patent Laid-Open Nos. 62-157863 and 3-67778, Japanese Utility Model Laid-Open Nos. 61-199472 and 3-121176.
FIGS. 11 to 14 show the tilt steering system disclosed in said Japanese Patent Laid-Open No. 3-67778. FIG. 11 is a side view thereof, wherein left side is the front side of the car and right side is the rear side of the car. FIG. 12 is a cross-sectional view of the system cut along 12--12 in FIG. 11. FIG. 13 is a cross-sectional view showing part of the system taken along 13--13 in FIG. 11. In this tilt steering system, a steering wheel (not shown: hereinafter, components not indicated by reference numerals are not shown in the figures) is fixed to the rear end of a steering shaft. The steering shaft is rotatably held in a steering column 1, whose front end portion is rockably set around a cross-shaft (first cross-shaft). An up and down or vertically shifting bracket 2, which is a metal plate folded into a U-shape is fixed by welding to the lower part of the middle portion of said steering column 1. A fixed bracket 3, to which the vertically shifting bracket 2 is abutted, is fixed to the car body.
The fixed bracket 3 consists of a pair of vertical panels 4a and 4b. Teeth 5 are formed on the rear edge of the upper part of the vertical panel 4a, along a circular arc which is convex toward the rear side and whose center coincides with the above-mentioned cross-shaft. An engaging stopper portion 6 is formed in the rear side of the lower part of the vertical panel 4a. Vertically elongated guide holes 7 are formed in the engaging stopper portion 6 and in the rear side of the lower part of the other vertical panel 4b corresponding to the engaging stopper portion. The guide holes 7 are formed along a circular arc whose center coincides with the cross-shaft. A second cross-shaft 8 penetrating the side walls of said vertically shifting bracket 2 has its ends idly engaged in respective guide holes 7. An engaging stopper lever or latch lever 9 located between the outer side of the vertically shifting bracket 2 and the inner side of the engaging stopper portion 6 pivots on one end of the second cross-shaft 8. A cam hole 10 is formed in the other side of the engaging latch lever 9. The cam hole 10 is not formed along a circular arc whose center coincides with a third cross-shaft 12, on which the front end of a tilt lever 11 pivots. Accordingly, the distance from the third cross-shaft 12 to the cam hole 10 gradually varies with respect to the positions along the rim of the cam hole 10. Further, rockable teeth 13 are formed on the front edge of the upper part of the latch lever 9 constructed as described above, such that the rockable teeth 13 can be engaged with and disengaged from the fixed teeth 5.
The third cross-shaft 12 is provided in the front side of the middle part of the vertical panel 4a, which is one of the vertical panels constituting the fixed bracket 3. As mentioned above, the front end of the tilt lever 11 pivots on the third cross-shaft 12. An engaging pin 16 projected from the middle portion of the inner side of the tilt lever 11 is loosely engaged in the cam hole 10. If the tilt lever 11 is rotated counter-clockwise (see FIG. 11) around the third cross-shaft 12 and the engaging pin 16 is shifted upward along the cam hole 10, the latch lever 9 is rotated clockwise around the second cross-shaft 8 so that the rockable teeth 13 formed on the front edge of the upper part of the latch lever 9 are separated from the fixed teeth 5 formed on the rear edge of the vertical panel 4a of the fixed bracket 3.
On the other hand, if the tilt lever 11 is rotated clockwise (in FIG. 11) around the third cross-shaft 12 and the engaging pin 16 is shifted downward along the cam hole 10, the latch lever 9 is rotated counter-clockwise around the second cross-shaft 8 so that the rockable teeth 13 formed on the front edge of the upper part of the latch lever engage the fixed teeth 5 formed on the rear edge of the vertical panel 4a of the fixed bracket 3. An extension spring 14 is connected between one end of the second cross-shaft 8 and the middle portion of the tilt lever 11 in order to give a clockwise bias (see FIG. 11) to the tilt lever 11, whereby the fixed teeth 5 and the rockable teeth 13 always engage each other as long so no external force is applied.
In the conventional tilt steering system constructed as described above, height of the steering wheel is adjusted according to the constitution or the like of the driver as follows. By lifting up a grip portion 15 provided at the peripheral end of the tilt lever 11, the tilt lever 11 is rotated counter-clockwise (see FIG. 11), against the force given by the extension spring 14, around the third cross-shaft 12. At that time, as shown in FIG. 14, the engaging pin 16 projected from the middle portion of the inner side of the tilt lever 11 is shifted up to the upper end portion 10a of the cam hole 10 formed in the upper end of the engaging stopper lever 9.
As a result, the rockable teeth 13 formed on the front edge of the upper part of said latch lever 9 retreat from the fixed teeth 5 formed on the rear edge of the vertical panel 4a of the fixed bracket 3. Thus, the rockable teeth 13 disengage from the fixed teeth 5 so that the vertically shifting bracket 2 fixed to the steering column 1 can be shifted up/down with respect to the fixed bracket 3 fixed to the car body.
Subsequently, the steering wheel in the above-mentioned state is adjusted to an arbitrary height in a range where the ends of the second cross-shaft can move in the pair of respective guide holes 7. As the steering wheel is shifted up and down, the steering column 1 is rocked around said first cross-shaft. At the same time, the vertically shifting bracket 2 fixed to the lower part of the middle portion of the steering column 1 is shifted up and down between the pair of vertical panels 4a and 4b constituting the fixed bracket 3, and the engaging stopper lever 9 whose bottom end pivots on the second cross-shaft penetrating the vertically shifting bracket 2 is also shifted up and down.
After adjusting the height of the steering wheel, the tilt lever 11 is rotated clockwise (see FIG. 11) around the third cross-shaft 12 so that the engaging pin 16 projected from the inner side of the tilt lever 11 is shifted downward along the cam hole 10 formed in the peripheral end of the latch lever 9. As a result, the rockable teeth 13 formed on the front edge of the upper part of the latch lever 9 approach the fixed teeth 5 formed on the rear edge of the vertical panel 4a of the fixed bracket 3. Thus, the rockable teeth 13 engage the fixed teeth 5, and the vertically shifting bracket 2 fixed to the steering column 1 cannot be shifted up or down with respect to the fixed bracket 3 fixed to the car body, thereby holding said steering wheel at adjusted height.
In the conventional construction shown in FIGS. 11 to 14, though it is possible to adjust height of the steering wheel without increasing the amount of operation of the tilt lever, rigidity of the steering wheel whose height is adjusted is not sufficient. More particularly, the vertically shifting bracket 2 fixed to the steering column is fixed to the fixed bracket 3 fixed to the car body only by engagement of the fixed teeth 5 and the rockable teeth 13, wherein the vertical panels 4a and 4b of the fixed bracket 3 are not pressed against the side surfaces of the vertically shifting bracket 2.
Therefore, even when the steering wheel whose height is adjusted is fixed, the vertically shifting bracket 2 tends to rattle in the fixed bracket 3, whereby the driver who handles the steering wheel feels undesirable uncertainty. The construction disclosed in the above-mentioned the Japanese Patent Laid-Open No. 62-157863 also has the same shortcoming.
In contrast, the Japanese Utility Model Laid-Open No. 61-199472 discloses a construction in which the steering wheel whose height is adjusted is fixed by pressing the vertical panels of the fixed bracket against both sides of the vertically shifting bracket. In this construction, however, the steering wheel whose height is adjusted is fixed only by friction between both sides of the vertically shifting bracket and respective inner side of the vertical panels of the fixed bracket, Thus, a larger amount of operation of the tilt lever is required to obtain sufficient rigidity. This is undesirable from the standpoint of usability. Also, because fixation is performed only with friction, when strong force is given to the steering wheel, as, for example, in the case of a car crash, the steering wheel can deviate from its set position. In order to ensure the effect of an air bag device installed in the steering wheel for protecting the driver in a car crash, such deviation should be avoided.
To solve the above problem, in construction disclosed in the Japanese Utility Model Laid-Open No. 3-121176, not only do the vertical panels of the fixed bracket pressure-weld both sides of the vertically shifting bracket, but two sets of working teeth engage with each other to fix the steering wheel whose height is adjusted.
In the above-mentioned constitution, however, the upper end of a rockable arm pivots on the fixed bracket, and after tightening up a tilt bolt in a tilt nut, working teeth formed in said rockable arm engage with working teeth formed in the vertically shifting bracket against a spring force. Accordingly, problems arise in that, for example, the rockable arm becomes longer, and engagement of the two sets of working teeth becomes insecure.